1. Field of the Invention
The present invention relates to Streptomyces sp. R-5; a plant disease control agent comprising the strain as an active ingredient; a method for producing disease-resistant plants characterized by inoculating the strain to the plants; and a phytoalexin inducer agent comprising the strain as an active ingredient.
2. Prior Art
Ornamental plants have been grown in many ways such as soil culture in plastic green house, pot culture, water culture, gravel culture and rock wool culture, or open culture. However in such cultures, ornamental plants infected with pathogenic microorganisms often lose their commercial value. Various methods have been devised to control such disease damages. For example, methods employed in soil culture include sterilization of plants with agricultural chemicals, such as TPN (tetrachloroisophthalonitrile), captan, eclomezol, metalaxyl, mepronil, and PCNB (pentachloronitrobenzene) agent; disinfection of plants with solar heat wherein the soil surface layer where plant pathogenic microorganisms are present is covered by a black vinyl sheet; and fumigation of the deep ground portion of soil using agricultural chemicals, such as methyl bromide and chlorpicrate, which generate toxic gas. Methods tried in water culture, gravel culture, and rock wool culture, include disinfection of the entire installation using formalin or sodium hypochlorite or mixing culture fluid with eclomezol or TPN agent.
Currently, ornamental plants, such as rhododendron and mountain laurel, members of Ericaceae family, are cultivated as follows. Seedlings of ornamental plants are raised in media in glass or plastic containers, transplanted onto a substrate such as soil, vermiculite or sphagnum, then acclimatized to an outdoor environment. During these cultivation steps, seedlings are raised on artificial media under sterile conditions so that only a few of them suffer from plant pathogenic microorganisms. Immediately after acclimation starts, however, plants can become afflicted by plant pathogenic microorganisms present around the plants. In some cases entire seedlings can wilt or be killed. To avoid this, after seedlings are taken out of their containers, they are transplanted into nursery beds consisting of soil or vermiculite and sphagnum, and agricultural chemicals such as metalaxyl, captan, validamycin, and TPN are applied to the seedlings. Even after seedlings are planted in fields, benomyl, TPN, maneb, mancozeb, metalaxyl and the like are often applied to the seedlings for disease control. Cultivation of ornamental plants using such tissue culture seedlings is conducted in Southeast Asia. For example in Thailand, large amounts of agricultural chemicals are used for disease control. There is concern that potted plants imported and brought into households from such countries can affect the human body with volatile agricultural chemicals.
Measures for plant disease control, independent of agricultural chemicals, such as manuring practice, raising resistant varieties, and eliminating a source of secondary infection have been tested. However, there is a limit to the efficacy of such indirect measures. Currently, there is no known effective method other than treatment with agricultural chemicals, and elimination or incineration of infected plants. Gas used for disinfecting soil, such as methyl bromide and chlorpicrate is toxic to the human body and tends to cause air pollution. Recently, strict regulations have reduced the toxicity of agricultural chemicals, but on the other hand, have led to an increase in the number of times that such agricultural chemicals are used. There is a danger that, as a result this will lead to environmental contamination, such as soil and air pollution, which in turn is linked to serious problems, such as hormone-disrupting substances that adversely affect future generations. There is a fear that repetitive use of agricultural chemicals may induce pathogenic microorganisms to become resistant to the chemicals. Accordingly, safe methods for controlling plant diseases, which have low toxicity to humans and cause no environmental contamination, are required.
The present invention provides a biotic pesticide having low toxicity to humans and causing no environmental contamination. That is, the present invention provides Streptomyces sp. R-5; a plant disease control agent comprising this strain as an active ingredient; a method for producing a disease-resistant plant comprising inoculating the strain to plants; and a phytoalexin inducer agent comprising the strain as an active ingredient.
The inventors have succeeded in producing a disease-resistant plant by inoculation of Streptomyces sp. R-5 isolated from rhododendron as a result of diligent research on the above problems.
The present invention relates to a plant disease control agent comprising Streptomyces spp. [for example, Streptomyces sp. R-5(FERM BP-7179)] as an active ingredient. R-5 (deposit number: FERM BP-7179) is deposited under the Budapest Treaty at National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology, at 1-3, Higashi 1-chome, Tsukuba-shi, Ibaraki-ken 305-8566 JAPAN. The plants subjected to administration of the plant disease control agent include those in the state of seedlings. The types of plants subjected to the administration of the plant disease control agent include those belonging to the family Ericaceae, for example Rhododendron.
Further, the present invention relates to a method for producing a disease-resistant plant, characterized by inoculating Streptomyces spp. [for example, Streptomyces sp. R-5(FERM BP-7179)] into a plant. Here plants subjected to administration of the plant disease control agent include those in the state of seedlings. Types of plants subjected to the administration of the plant disease control agent include those belonging to the family Ericaceae, for example rhododendron and mountain laurel.
Furthermore, the present invention relates to a phytoalexin inducer agent comprising Streptomyces spp. [for example, Streptomyces sp. R-5(FERM BP-7179)] as an active ingredient.